Sure, it's not going to discourage someone that is very actively looking elsewhere already. But for people on the fence? And the people that would follow them if they made the jump? That's who this is aimed at. And who knows? For the folks already looking to get out, if the first one or two opportunities to come their way don't work out, maybe they'll decide to stay too.

This is especially true for anyone looking to jump ship mostly for the money: If someone wants to jump ship for an extra 40k-50k, then giving them 30k makes the difference pretty negligible, all else being equal.